A loxP-flanked PGKneo cassette site was inserted upstream of exon 2 and a third loxP site was inserted downstream of exon 2. Cre-mediated recombination removed the neo cassette. Exon 2 was subsequently removed from properly targeted mice by crossing to transgenic mice carrying Tg(EIIa-cre)C5379Lmgd. (J:94077)